<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>Document</title>
  </head>
  <body>
    <script>
      function getResult() {
        // 该函数没有return
      }
      console.log(getResult());	// 输出结果：undefined
    </script>
  </body>
</html>